Billion Oyster Project

Fecal Coliform and Numerical Extrapolation (Is it safe to drink?)


Water Quality Lessons



Class Periods




Subject Areas


This lesson opens with a hands-on lab demo about "parts per million." The students watch as food coloring gets more and more diluted until there is one part of food coloring per million parts of liquid. Then, the students learn a bit about fecal coliform. Finally, students do an activity where they determine whether or not water is safe to drink by using unit conversions and looking at actual situations.


  • Convert units
  • Describe "parts per million"

Materials and Resources


  • Test tube well with at least 6 test tubes in each
  • Food coloring
  • Calculators

Before you get started

Tips for Teachers

  • For the dilution activity, you can do it either as a class or have student groups do it together. You can also modify the worksheet, depending on how much scaffolding your students need. They can complete only the questions, only the table, or both.
  • Many assumptions were made and much rounding was done in order to allow the math to be done more easily. This lesson is meant to be an open inquiry activity.
  • If you would like to teach unit conversions explicitly, I would recommend this method: However, I think students would strongly benefit from needing to work together and struggle in order to figure out how to convert the units on their own. If unit conversion needs to be taught, make it a different day.
  • For this lesson, give them the time and space to struggle with the units and answer the questions on their own.


Enterococcus  is often measured in parts per million or parts per billion. This lesson looks at how big a part per million is.

“Fecal coliform (enterococcus)  bacteria are the most common microbiological contaminants of natural waters. Fecal coliform live in the digestive tracts of warm-blooded animals, including humans, and are excreted in the feces. Although most of these bacteria are not harmful and are part of the normal digestive system, some are pathogenic to humans. Those that are pathogenic can cause disease such as gastroenteritis, ear infections, typhoid, dysentery, hepatitis A, and cholera.  

A fecal coliform test is used to determine whether water has been contaminated with fecal matter. The presence of fecal coliform indicates the possible presence of organisms that can cause illness.”

Instruction Plan


Dilution Demo:

  1. Put one drop of food coloring into a test tube with 9 drops of water. That is your first solution.
  2. Then take one drop of that solution and put it into another test tube with 9 more drops of clear water. That is your second solution.
  3. Complete this process four more times until you have 6 solutions or 1 part food coloring per million parts water.


Students get and complete How Big is a Part Per Million? (see Tips for Teachers above.)


  1. Explain: Parts per million is the most commonly used measurement for fecal coliform and that it is the same as 1g/m3. One common safe standard for drinking water is that drinking water is safe if there is one enterococcus or less per 100mL of water (about one part per billion). The common safe standard for swimming is 60 enterococcus per 100 mL.  
  2. This is a good time to consider one part per million and how the solution looked clear. Ask students if they would be able to identify if water is clean by looking at it.
  3. Discuss situations that students might encounter where the water quality might not be good. How would they know?
  4. Explain: Water must be tested to ensure good water quality.


  1. Students get YOU Are a Water Quality Detective! 
  2. Students will examine 3 situations and decide whether or not the water is safe to bathe in and to drink.
  3. Explain: The drinking water standard is very high.  Should the swimming standard be as high?  What should the swimming standard be?


  1. Follow up with a class discussion.
  2. Examine the students results.
  3. Explain: Water quality testing is complex and has no easy answers. Enterococcus is only an indicator, it does not signify all of the microbes in the water.
  4. Discuss other mitigating factors (do particles settle on the bottom, what if the pooper was sick, what if you got water in your eye, etc.)


CCLS - ELA Science & Technical Subjects

    • Compare and contrast the information gained from experiments, simulations, video, or multimedia sources with that gained from reading a text on the same topic.

CCLS - Mathematics

    • Write and evaluate numerical expressions involving whole-number exponents.

NGSS - Cross-Cutting Concepts

  • Influence of Engineering, Technology, and Science on Society and the Natural World

    • All human activity draws on natural resources and has both short and long-term consequences, positive as well as negative, for the health of people and the natural environment.

NGSS - Disciplinary Core Ideas

  • ESS3.C: Human Impacts on Earth Systems

    • Human activities have significantly altered the biosphere, sometimes damaging or destroying natural habitats and causing the extinction of other species. But changes to Earth’s environments can have different impacts (negative and positive) for different living things.
    • Typically as human populations and per-capita consumption of natural resources increase, so do the negative impacts on Earth unless the activities and technologies involved are engineered otherwise.

NGSS - Science and Engineering Practices

  • Analyzing and Interpreting Data

    • Analyze and interpret data to provide evidence for phenomena.

NYC Science Scope & Sequence - Units

  • Grade 8, Unit 4

    • Humans and the Environment: Needs and Tradeoffs

NYS Science Standards - Key Ideas

  • LE Key Idea 6

    • Plants and animals depend on each other and their physical environment.
  • LE Key Idea 7

    • Human decisions and activities have had a profound impact on the physical and living environment

NYS Science Standards - Major Understandings

    • Matter is transferred from one organism to another and between organisms and their physical environment. Water, nitrogen, carbon dioxide, and oxygen are examples of substances cycled between the living and nonliving environment.
    • The environment may contain dangerous levels of substances (pollutants) that are harmful to organisms. Therefore, the good health of environments and individuals requires the monitoring of soil, air, and water, and taking steps to keep them safe.
    • In ecosystems, balance is the result of interactions between community members and their environment.
    • The environment may be altered through the activities of organisms. Alterations are sometimes abrupt. Some species may replace others over time, resulting in long- term gradual changes (ecological succession).
    • Since the Industrial Revolution, human activities have resulted in major pollution of air, water, and soil. Pollution has cumulative ecological effects such as acid rain, global warming, or ozone depletion. The survival of living things on our planet depends on the conservation and protection of Earth’s resources.

NYS Science Standards - MST

    • Students will access, generate, process, and transfer information using appropriate technologies.
    • Students will understand the relationships and common themes that connect mathematics, science, and technology and apply the themes to these and other areas of learning.
    • Students will apply the knowledge and thinking skills of mathematics, science, and technology to address real-life problems and make informed decisions.